1. Field of the Invention
The present invention relates to an image forming apparatus, particularly the image forming apparatus formed so that a sheet cassette is drawably mounted onto a cassette housing portion formed in a main body of the image forming apparatus.
2. Description of the Related Art
An example of image forming apparatuses such as conventional facsimile machines, copying machines, and printers includes an image forming apparatus which is formed so that the sheet cassette which houses the sheet is drawably mounted onto the cassette housing portion formed in the main body of the image forming apparatus. In such an image forming apparatus, the sheet housed in the sheet cassette is sequentially conveyed to an image forming portion at the time of image formation and images are formed on the sheet in the image forming portion.
The conventional image forming apparatuses have a drawer apparatus which drawably mounts the sheet cassette. FIG. 6 illustrates the structure of such a drawer apparatus.
The drawer apparatus is formed opposite to the inner wall surface of the cassette housing portion of the main body of the image forming apparatus (not shown) and has a frame rail 20 which is a guide when a sheet cassette 2 is pulled out. Further, the drawer apparatus is formed on the wall surface of both sides of the sheet cassette 2 opposite to the frame rail 20 and has a cassette rail 3 which is a guide when the sheet cassette 2 is pulled out.
The frame rail 20 includes an outer rail 7 fixed to the inner wall surface of the cassette housing portion, an inner rail 8 which is slidably held by the outer rail 7 and in which a locking member 9 is formed in a downstream end in a pull out direction illustrated by an arrow (hereinafter referred to as pull out direction). When the sheet cassette 2 is moved, the cassette rail 3 which is an engaging portion is engaged with the inner rail 8 which is a rail member. Then, both rails are moved along the inner rail 8 while the movement of the sheet cassette 2 in a sliding direction is regulated.
A roller bearing member 10 which rotates on an axis 10a along the cassette rail 3 of the sheet cassette 2 is formed in the downstream end of the inner rail 8 in the pull out direction so as to allow the sheet cassette 2 to be pulled out smoothly. In order to allow the sheet cassette 2 to be pulled out smoothly, rotating roller bearing members 4 and 5 are formed on the wall surface of both sides of the sheet cassette 2 along an upper guide surface 8a of the inner rail 8 and a lower guide surface 8b. 
The roller bearing members 4 and 5 are rotatably held by fixed shafts 4a and 5a provided at a roller bearing support member 6 which has a part of the cassette rails 3. A locking claw 11 which is locked by the locking member 9 of the inner rail 8 when the sheet cassette 2 is pulled out is formed in the downstream end of the roller bearing support member 6 in the pull out direction.
In such a drawer apparatus, when the sheet cassette 2 is pulled out, for example, for housing the sheet, the locking claw 11 which is a drawer stop portion provided at the roller bearing support member 6 is locked by the locking member 9 which is a stop portion formed on the lower guide surface 8b of the inner rail 8 as shown in FIG. 7. Further, when the sheet cassette 2 is pulled out, the sheet cassette 2 slides integrally with the inner rail 8 along the outer rail 7 under the condition that the locking claw 11 is locked by the locking member 9.
Thus, the sheet cassette 2 is pulled out while the inner rail 8 is integrally pulled out. Thereafter, a stopper (not shown) which is provided at the inner rail 8 is locked by the outer rail 7, which allows the sheet cassette 2 to be stopped in the condition that the inner rail 8 is pulled out. The sheet can be housed in the sheet cassette without separating from the main body of the image forming apparatus by pulling out the sheet cassette 2 in such a manner.
When the sheet cassette 2 is detached from the main body of the image forming apparatus, the downstream of the sheet cassette 2 in the pull out direction is lifted upward in the condition that the sheet cassette 2 is pulled out from the main body of the image forming apparatus as shown in FIG. 8. Thus, the engagement of the locking claw 11 of the sheet cassette 2 and the locking member 9 of the inner rail 8 is separated. The sheet cassette 2 can be detached (drawn out) from the main body of the image forming apparatus by pulling out the sheet cassette 2 under the condition.
Here, an abutting portion 11a against the locking member 9 of the locking claw 11 of the roller bearing support member 6 (shown in FIG. 8) and an abutting portion 9a against the locking claw 11 of the locking member 9 of the inner rail 8 are inclined so as to guide the movement in a take out direction of the sheet cassette 2, namely, the movement obliquely upward. Thus, in taking out the sheet cassette 2, when the downstream of the sheet cassette 2 in the pull out direction is lifted, the sheet cassette 2 is lifted obliquely upward while being guided by the inclination of the abutting portion 11a of the locking claw 11 and the abutting portion 9a of the locking member 9.
Further, a concave portion 6a is formed on the upper surface of the roller bearing support member 6 (cassette rail 3) so that the roller bearing support member 6 (cassette rail 3) does not abut against the inner rail 8 when the sheet cassette 2 is lifted in such a manner.
For example, in the case where the image forming apparatus is placed in a low position, when a user tries to pull out the sheet cassette 2, the user needs to grip a handle of the sheet cassette 2 to pull out the sheet cassette 2 as it is tilted. Here, in the case of such a structure of the drawer apparatus, when the user tries to pull out the sheet cassette 2 as it is tilted, the locking claw 11 of the sheet cassette 2 does not abut against the locking member 9 of the inner rail 8 as shown in FIG. 8 and the sheet cassette 2 is drawn out.
An example of the structure for solving such problems includes a structure having a stop member which allows the sheet cassette 2 to be stopped at a predetermined drawing position without drawing out when the sheet cassette 2 is pulled out. The technique is disclosed in Japanese Patent No. 3571910.
However, in the case of conventional image forming apparatuses having such a stop member, when the user draws out the sheet cassette, the stop member has to be moved from the position where the sheet cassette is stopped at the drawing position to the position where the sheet cassette can be drawn out.
When the drawn out sheet cassette is mounted, the stop member has to be moved from the position where the sheet cassette can be drawn out to the position where the sheet cassette is stopped at the drawing position. Therefore, when the sheet cassette is drawn out or mounted, the operation is complicated.